1. Field of the Invention
The present invention relates to an evaporated fuel treatment device, and more particularly to an evaporated fuel treatment device for treating evaporated fuel generated in a fuel tank without being released into the atmosphere.
2. Background Art
As disclosed in, for example, Japanese Patent Laid-Open No. 2001-193580, an evaporated fuel treatment device is known that includes a canister for adsorbing evaporated fuel generated in a fuel tank. In this device, the fuel tank communicates with the canister via a charge control valve and communicates with an intake passage of an internal combustion engine via a tank pressure control valve.
In the conventional device, the tank pressure control valve is opened to introduce induction negative pressure into the fuel tank, thus keeping tank internal pressure in a negative state, during operation of the internal combustion engine. Keeping the tank internal pressure in the negative state as described above prevents the evaporated fuel generated in the fuel tank from being released into the atmosphere.
In the conventional device, if abnormality occurs in the charge control valve placed between the fuel tank and the canister, proper treatment of the evaporated fuel generated in the fuel tank becomes difficult. Thus, this device requires diagnosing whether the charge control valve normally functions.
To meet this requirement, the conventional device diagnoses the charge control valve by the below described method. Specifically, when diagnosing the charge control valve, the device first closes both the charge control valve and the tank pressure control valve and forms a state where the canister is opened to the atmosphere under a situation where the tank internal pressure is made negative by normal control. Then, the device issues a valve opening instruction to the charge control valve, and determines whether a change occurs in the tank internal pressure between before and after the instruction.
If the charge control valve is properly opened in the state where the tank internal pressure is negative, air flows from the canister into the fuel tank to increase the tank internal pressure. On the other hand, if the charge control valve remains closed, that is, if closing failure occurs in the charge control valve, no change occurs in the tank internal pressure between before and after the valve opening instruction. Thus, if there in no sign of significant increase in the tank internal pressure between before and after the instruction, the conventional device determines that the closing failure occurs in the charge control valve. According to the above described procedure, the conventional device can accurately detect the closing failure of the charge control valve.